Field of the Invention
The invention describes an article made of a flexible rubber and/or plastic as well as a process for making this article.
Many flexible articles that are untreated on the surface, particularly those made of plastic and rubber, have a relatively high degree of friction resistance in relation to human skin. This is why untreated rubber gloves, for example, are almost impossible to put on. In order to make it easier to put these gloves on, glove powder (e.g. starch powder, talcum, etc.) is conventionally deposited as a parting compound on the inside of the glove. The use of powder, though, is particularly problematic in the medical field because residual powder can lead to granule formation if it gets into open wounds. Another important application field for powder-free products is the electronics industry.
A classic method for making articles of rubber and in particular, gloves that are slippery in relation to human skin without the use of powder, involves surface chlorination. In this connection, the article is treated with aqueous, chlorine gas-containing mediums and is then washed. Primarily, this produces a favorable slipperiness in relation to dry human skin, but this surface chlorination synthetically alters the polymer structure and thus produces a distinct diminishing of the physical and chemical properties of the article (strength, tear elasticity, water swelling, storability, etc.). However, surface-treated gloves of this kind are also usually difficult to put on with wet hands.
Coating with hydrogels represents an alternative surface treatment. Some hydrogels of this kind have been known for a long time. For example, these are polyurethane, polyvinylpyrrolidone, polyhydroxyethylacrylate or polyhydroxymethacrylate, polyhydroxypropylacrylate or polyhydroxypropylmethacrylate, and are copolymers with one another or with acrylic acid or methacrylic acid, acrylic ester or methacrylic ester, or vinylpyridine.
A coating of this kind has been disclosed by U.S. Pat. No. 3,813,695, which describes a dipped rubber glove that is coated on the inside with a hydrogel polymer such as polyvinylpyrrolidone, polyhydroxyethacrylate or polyhydroxymethacrylate, polyhydroxypropylacrylate or polyhydroxypropylmethacrylate, and copolymers of these with one another or with acrylic acid or methacrylic acid. The preferred hydrogel polymer is a copolymer of 2-hydroxyethylmethacrylate with methacrylic acid or with 2-ethylhexylacrylate or a ternary copolymer of 2-hydroxyethylmethacrylate, methacrylic acid and 2-ethylhexylacrylate.
A known manufacturing process is disclosed by U.S. Pat. No. 4,482,577. This patent discloses the coating of a flexible, vulcanized surgical glove with a hydrophilic polymer, by means of which the depositing of powder on the inside of the glove can be omitted. The copolymer used in this instance is comprised of a mixture of 2-hydroxyethylmethacrylate and 2-ethylhexylacrylate.
Another process according to U.S. Pat. No. 4,100,309 discloses the depositing of a slippery coating comprised of a polyurethane-polyvinylpyrrolidone complex. Normally with these products or processes, the hydropolymer is deposited on the product together with a hardener in dissolved form, then the solvent is removed by drying, wherein the polymer layer is hardened, thus forming a hydrogel coating.
Other known embodiments disclose the use of vinylidene halogenide lattices or vinyl halogenide lattices for producing a slip coating on rubber articles, e.g. U.S. Pat. No. 5,069,965, where the slippery quality is mostly achieved by means of polymers that contain chlorine.
DE 26 28 059-C and U.S. Pat. No. 4,082,862 disclose the use of diverse latex mixtures for producing a slip coating. In particular, mixtures comprised of at least two latex types are used in this connection, wherein a latex type with a high elasticity is used as a bonding agent and a latex type with a high degree of hardness or low elasticity is used to obtain a sufficient slipperiness. These recipes are usually more or less favorable compromises between slipperiness, sufficient film flexibility, and adhesion of the film to the rubber product. In particular, with the use of the slip coating in very flexible, highly elastic rubber articles, there are often problems in this connection to the effect that the slip coatings used either begin to detach from the foundation when stretched or do not have a satisfactory slipperiness in actual use.
In the process according to EP 0 681 912-A2, the slip coating is comprised of a copolymer latex, which is fixed to the carrier layer with the aid of a coagulation step. The latex is comprised of a copolymer that contains a significant portion of hydrophilic monomer components.
U.S. Pat. No. 4,143,109 describes another method for producing slipperiness in relation to skin with powder-free medical gloves made of natural latex. In this instance, bonded cornstarch particles or polyethylene particles are deposited in a carrier layer, wherein the carrier layer is thinner than the diameter of the particles and the particles protrude from the surface. The powder particles bonded in this manner produce a sufficient slipperiness of the glove interior. This embodiment for achieving slipperiness in relation to skin has problems when the product is stretched to a great degree, which is inevitable when putting on latex medical gloves: The surface-bonded particles detach easily and the powder-free nature is no longer assured.
All of the above-described powder-free articles can only be produced with satisfactory product properties only under the most precise adherence to the affiliated process requirements and material recipes. While a favorable slipperiness of the surfaces in relation to dry skin is usually achieved with ease, very often there are difficulties in the reproducibility with regard to wet slipperiness. In particular with thin-walled flexible articles, which must have favorable slipperiness even when stretched to a great degree, it often takes years of high-precision optimization on the part of the manufacturer, who usually has to adopt compromises with regard to diverse product properties. Despite the use of polymeric slip coating hydrogels, the surface is frequently lightly chlorinated. Other manufacturers, in spite of the polymer slip coatings, use additional small quantities of glove powder. Still other producers see themselves as confronted with constant fluctuations with regard to the wet slipperiness of their products.